Redirecting raltitrexed from cancer cell thymidylate synthase to Mycobacterium tuberculosis phosphopantetheinyl transferase.

There is a compelling need to find drugs active against Mycobacterium tuberculosis (Mtb). 4'-Phosphopantetheinyl transferase (PptT) is an essential enzyme in Mtb that has attracted interest as a potential drug target. We optimized a PptT assay, used it to screen 422,740 compounds, and identified raltitrexed, an antineoplastic antimetabolite, as the most potent PptT inhibitor yet reported. While trying unsuccessfully to improve raltitrexed's ability to kill Mtb and remove its ability to kill human cells, we learned three lessons that may help others developing antibiotics. First, binding of raltitrexed substantially changed the configuration of the PptT active site, complicating molecular modeling of analogs based on the unliganded crystal structure or the structure of cocrystals with inhibitors of another class. Second, minor changes in the raltitrexed molecule changed its target in Mtb from PptT to dihydrofolate reductase (DHFR). Third, the structure-activity relationship for over 800 raltitrexed analogs only became interpretable when we quantified and characterized the compounds' intrabacterial accumulation and transformation.

APR-246 increases tumor antigenicity independent of p53.

We previously reported that activation of p53 by APR-246 reprograms tumor-associated macrophages to overcome immune checkpoint blockade resistance. Here, we demonstrate that APR-246 and its active moiety, methylene quinuclidinone (MQ) can enhance the immunogenicity of tumor cells directly. MQ treatment of murine B16F10 melanoma cells promoted activation of melanoma-specific CD8+ T cells and increased the efficacy of a tumor cell vaccine using MQ-treated cells even when the B16F10 cells lacked p53. We then designed a novel combination of APR-246 with the TLR-4 agonist, monophosphoryl lipid A, and a CD40 agonist to further enhance these immunogenic effects and demonstrated a significant antitumor response. We propose that the immunogenic effect of MQ can be linked to its thiol-reactive alkylating ability as we observed similar immunogenic effects with the broad-spectrum cysteine-reactive compound, iodoacetamide. Our results thus indicate that combination of APR-246 with immunomodulatory agents may elicit effective antitumor immune response irrespective of the tumor's p53 mutation status.

Arabinose- and xylose-modified analogs of 2',3'-cGAMP act as STING agonists.

Stimulator of interferon genes (STING) agonists are promising candidates for vaccine adjuvants and antitumor immune stimulants. The most potent natural agonist of STING, 2',3'-cyclic GMP-AMP (2',3'-cGAMP), is subject to nuclease-mediated inherent metabolic instability, thereby placing limits on its clinical efficacy. Here, we report on a new class of chemically synthesized sugar-modified analogs of 2',3'-cGAMP containing arabinose and xylose sugar derivatives that bind mouse and human STING alleles with high affinity. The co-crystal structures demonstrate that such analogs act as 2',3'-cGAMP mimetics that induce the "closed" conformation of human STING. These analogs show significant resistance to hydrolysis mediated by ENPP1 and increased stability in human serum, while retaining similar potency as 2',3'-cGAMP at inducing IFN-ß secretion from human THP1 cells. The arabinose- and xylose-modified 2',3'-cGAMP analogs open a new strategy for overcoming the inherent nuclease-mediated vulnerability of natural ribose cyclic nucleotides, with the additional benefit of high translational potential as cancer therapeutics and vaccine adjuvants.

Efficacy of HER2-Targeted Intraperitoneal 225Ac α-Pretargeted Radioimmunotherapy for Small-Volume Ovarian Peritoneal Carcinomatosis.

Epithelial ovarian cancer (EOC) is often asymptomatic and presents clinically in an advanced stage as widespread peritoneal microscopic disease that is generally considered to be surgically incurable. Targeted α-therapy with the α-particle-emitting radionuclide 225Ac (half-life, 9.92 d) is a high-linear-energy-transfer treatment approach effective for small-volume disease and even single cells. Here, we report the use of human epidermal growth factor receptor 2 (HER2) 225Ac-pretargeted radioimmunotherapy (PRIT) to treat a mouse model of human EOC SKOV3 xenografts growing as peritoneal carcinomatosis (PC). Methods: On day 0, 105 SKOV3 cells transduced with a luciferase reporter gene were implanted intraperitoneally in nude mice, and tumor engraftment was verified by bioluminescent imaging (BLI). On day 15, treatment was started using 1 or 2 cycles of 3-step anti-HER2 225Ac-PRIT (37 kBq/cycle as 225Ac-Proteus DOTA), separated by a 1-wk interval. Efficacy and toxicity were monitored for up to 154 d. Results: Untreated PC-tumor-bearing nude mice showed a median survival of 112 d. We used 2 independent measures of response to evaluate the efficacy of 225Ac-PRIT. First, a greater proportion of the treated mice (9/10 1-cycle and 8/10 2-cycle; total, 17/20; 85%) survived long-term compared with controls (9/27, 33%), and significantly prolonged survival was documented (log-rank [Mantel-Cox] P = 0.0042). Second, using BLI, a significant difference in the integrated BLI signal area to 98 d was noted between controls and treated groups (P = 0.0354). Of a total of 8 mice from the 2-cycle treatment group (74 kBq total) that were evaluated by necropsy, kidney radiotoxicity was mild and did not manifest itself clinically (normal serum blood urea nitrogen and creatinine). Dosimetry estimates (relative biological effectiveness-weighted dose, where relative biological effectiveness = 5) per 37 kBq administered for tumors and kidneys were 56.9 and 16.1 Gy, respectively. One-cycle and 2-cycle treatments were equally effective. With immunohistology, mild tubular changes attributable to α-toxicity were observed in both therapeutic groups. Conclusion: Treatment of EOC PC-tumor-bearing mice with anti-HER2 225Ac-PRIT resulted in histologic cures and prolonged survival with minimal toxicity. Targeted α-therapy using the anti-HER2 225Ac-PRIT system is a potential treatment for otherwise incurable EOC.

Dual Fluorescence Isogenic Synthetic Lethal Kinase Screen and High-Content Secondary Screening for MUC16/CA125-Selective Agents.

Significant strides have been made in the development of precision therapeutics for cancer. Aberrantly expressed glycoproteins represent a potential avenue for therapeutic development. The MUC16/CA125 glycoprotein serves as a biomarker of disease and a driver of malignant transformation in epithelial ovarian cancer. Previously, we demonstrated a proof-of-principle approach to selectively targeting MUC16+ cells. In this report, we performed a synthetic lethal kinase screen using a human kinome RNAi library and identified key pathways preferentially targetable in MUC16+ cells using isogenic dual-fluorescence ovarian cancer cell lines. Using a separate approach, we performed high-content small-molecule screening of six different libraries of 356,982 compounds for MUC16/CA125-selective agents and identified lead candidates that showed preferential cytotoxicity in MUC16+ cells. Compounds with differential activity were selected and tested in various other ovarian cell lines or isogenic pairs to identify lead compounds for structure-activity relationship (SAR) selection. Lead siRNA and small-molecule inhibitor candidates preferentially inhibited invasion of MUC16+ cells in vitro and in vivo, and we show that this is due to decreased activation of MAPK, and non-receptor tyrosine kinases. Taken together, we present a comprehensive screening approach to the development of a novel class of MUC16-selective targeted therapeutics and identify candidates suitable for further clinical development.

Mechanistic details of the actinobacterial lyase-catalyzed degradation reaction of 2-hydroxyisobutyryl-CoA.

Actinobacterial 2-hydroxyacyl-CoA lyase reversibly catalyzes the thiamine diphosphate-dependent cleavage of 2-hydroxyisobutyryl-CoA to formyl-CoA and acetone. This enzyme has great potential for use in synthetic one-carbon assimilation pathways for sustainable production of chemicals, but lacks details of substrate binding and reaction mechanism for biochemical reengineering. We determined crystal structures of the tetrameric enzyme in the closed conformation with bound substrate, covalent postcleavage intermediate, and products, shedding light on active site architecture and substrate interactions. Together with molecular dynamics simulations of the covalent precleavage complex, the complete catalytic cycle is structurally portrayed, revealing a proton transfer from the substrate acyl Cß hydroxyl to residue E493 that returns it subsequently to the postcleavage Cα-carbanion intermediate. Kinetic parameters obtained for mutants E493A, E493Q, and E493K confirm the catalytic role of E493 in the WT enzyme. However, the 10- and 50-fold reduction in lyase activity in the E493A and E493Q mutants, respectively, compared with WT suggests that water molecules may contribute to proton transfer. The putative catalytic glutamate is located on a short α-helix close to the active site. This structural feature appears to be conserved in related lyases, such as human 2-hydroxyacyl-CoA lyase 2. Interestingly, a unique feature of the actinobacterial 2-hydroxyacyl-CoA lyase is a large C-terminal lid domain that, together with active site residues L127 and I492, restricts substrate size to ≤C5 2-hydroxyacyl residues. These details about the catalytic mechanism and determinants of substrate specificity pave the ground for designing tailored catalysts for acyloin condensations for one-carbon and short-chain substrates in biotechnological applications.

Characterization of Phosphopantetheinyl Hydrolase from Mycobacterium tuberculosis.

Phosphopantetheinyl hydrolase, PptH (Rv2795c), is a recently discovered enzyme from Mycobacterium tuberculosis that removes 4'-phosphopantetheine (Ppt) from holo-carrier proteins (CPs) and thereby opposes the action of phosphopantetheinyl transferases (PPTases). PptH is the first structurally characterized enzyme of the phosphopantetheinyl hydrolase family. However, conditions for optimal activity of PptH have not been defined, and only one substrate has been identified. Here, we provide biochemical characterization of PptH and demonstrate that the enzyme hydrolyzes Ppt in vitro from more than one M. tuberculosis holo-CP as well as holo-CPs from other organisms. PptH provided the only detectable activity in mycobacterial lysates that dephosphopantetheinylated acyl carrier protein M (AcpM), suggesting that PptH is the main Ppt hydrolase in M. tuberculosis. We could not detect a role for PptH in coenzyme A (CoA) salvage, and PptH was not required for virulence of M. tuberculosis during infection of mice. It remains to be determined why mycobacteria conserve a broadly acting phosphohydrolase that removes the Ppt prosthetic group from essential CPs. We speculate that the enzyme is critical for aspects of the life cycle of M. tuberculosis that are not routinely modeled. IMPORTANCE Tuberculosis (TB), caused by Mycobacterium tuberculosis, was the leading cause of death from an infectious disease before COVID, yet the in vivo essentiality and function of many of the protein-encoding genes expressed by M. tuberculosis are not known. We biochemically characterize M. tuberculosis's phosphopantetheinyl hydrolase, PptH, a protein unique to mycobacteria that removes an essential posttranslational modification on proteins involved in synthesis of lipids important for the bacterium's cell wall and virulence. We demonstrate that the enzyme has broad substrate specificity, but it does not appear to have a role in coenzyme A (CoA) salvage or virulence in a mouse model of TB.

CSF1/CSF1R Signaling Inhibitor Pexidartinib (PLX3397) Reprograms Tumor-Associated Macrophages and Stimulates T-cell Infiltration in the Sarcoma Microenvironment.

Colony-stimulating factor 1 (CSF1) is a primary regulator of the survival, proliferation, and differentiation of monocyte/macrophage that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). Considering current advances in understanding the role of the inflammatory tumor microenvironment, targeting the components of the sarcoma microenvironment, such as TAMs, is a viable strategy. Here, we investigated the effect of PLX3397 (pexidartinib) as a potent inhibitor of the CSF1 receptor (CSF1R). PLX3397 was recently approved by the Food and Drug Administration (FDA) to treat tenosynovial giant cell tumor and reprogram TAMs whose infiltration correlates with unfavorable prognosis of sarcomas. First, we confirmed by cytokine arrays of tumor-conditioned media (TCM) that cytokines including CSF1 are secreted from LM8 osteosarcoma cells and NFSa fibrosarcoma cells. The TCM, like CSF1, stimulated ERK1/2 phosphorylation in bone marrow-derived macrophages (BMDMs), polarized BMDMs toward an M2 (TAM-like) phenotype, and strikingly promoted BMDM chemotaxis. In vitro administration of PLX3397 suppressed pERK1/2 stimulation by CSF1 or TCM, and reduced M2 polarization, survival, and chemotaxis in BMDMs. Systemic administration of PLX3397 to the osteosarcoma orthotopic xenograft model significantly suppressed the primary tumor growth and lung metastasis, and thus improved metastasis-free survival. PLX3397 treatment concurrently depleted TAMs and FOXP3+ regulatory T cells and, surprisingly, enhanced infiltration of CD8+ T cells into the microenvironments of both primary and metastatic osteosarcoma sites. Our preclinical results show that PLX3397 has strong macrophage- and T-cell-modulating effects that may translate into cancer immunotherapy for bone and soft-tissue sarcomas.

Anti-tumor effects of an ID antagonist with no observed acquired resistance.

ID proteins are helix-loop-helix (HLH) transcriptional regulators frequently overexpressed in cancer. ID proteins inhibit basic-HLH transcription factors often blocking differentiation and sustaining proliferation. A small-molecule, AGX51, targets ID proteins for degradation and impairs ocular neovascularization in mouse models. Here we show that AGX51 treatment of cancer cell lines impairs cell growth and viability that results from an increase in reactive oxygen species (ROS) production upon ID degradation. In mouse models, AGX51 treatment suppresses breast cancer colonization in the lung, regresses the growth of paclitaxel-resistant breast tumors when combined with paclitaxel and reduces tumor burden in sporadic colorectal neoplasia. Furthermore, in cells and mice, we fail to observe acquired resistance to AGX51 likely the result of the inability to mutate the binding pocket without loss of ID function and efficient degradation of the ID proteins. Thus, AGX51 is a first-in-class compound that antagonizes ID proteins, shows strong anti-tumor effects and may be further developed for the management of multiple cancers.

Engineered Cells as a Test Platform for Radiohaptens in Pretargeted Imaging and Radioimmunotherapy Applications.

Pretargeted imaging and radioimmunotherapy approaches are designed to have superior targeting properties over directly targeted antibodies but impose more complex pharmacology, which hinders efforts to optimize the ligands prior to human applications. Human embryonic kidney 293T cells expressing the humanized single-chain variable fragment (scFv) C825 (huC825) with high-affinity for DOTA-haptens (293T-huC825) in a transmembrane-anchored format eliminated the requirement to use other pretargeting reagents and provided a simplified, accelerated assay of radiohapten capture while offering normalized cell surface expression of the molecular target of interest. Using binding assays, ex vivo biodistribution, and in vivo imaging, we demonstrated that radiohaptens based on benzyl-DOTA and a second generation "Proteus" DOTA-platform effectively and specifically engaged membrane-bound huC825, achieving favorable tumor-to-normal tissue uptake ratios in mice. Furthermore, [86Y]Y-DOTA-Bn predicted absorbed dose to critical organs with reasonable accuracy for both [177Lu]Lu-DOTA-Bn and [225Ac]Ac-Pr, which highlights the benefit of a dosimetry-based treatment approach.

Targeting eIF4A-Dependent Translation of KRAS Signaling Molecules.

Pancreatic adenocarcinoma (PDAC) epitomizes a deadly cancer driven by abnormal KRAS signaling. Here, we show that the eIF4A RNA helicase is required for translation of key KRAS signaling molecules and that pharmacological inhibition of eIF4A has single-agent activity against murine and human PDAC models at safe dose levels. EIF4A was uniquely required for the translation of mRNAs with long and highly structured 5' untranslated regions, including those with multiple G-quadruplex elements. Computational analyses identified these features in mRNAs encoding KRAS and key downstream molecules. Transcriptome-scale ribosome footprinting accurately identified eIF4A-dependent mRNAs in PDAC, including critical KRAS signaling molecules such as PI3K, RALA, RAC2, MET, MYC, and YAP1. These findings contrast with a recent study that relied on an older method, polysome fractionation, and implicated redox-related genes as eIF4A clients. Together, our findings highlight the power of ribosome footprinting in conjunction with deep RNA sequencing in accurately decoding translational control mechanisms and define the therapeutic mechanism of eIF4A inhibitors in PDAC. SIGNIFICANCE: These findings document the coordinate, eIF4A-dependent translation of RAS-related oncogenic signaling molecules and demonstrate therapeutic efficacy of eIF4A blockade in pancreatic adenocarcinoma.

A Self-Assembling and Disassembling (SADA) Bispecific Antibody (BsAb) Platform for Curative Two-step Pretargeted Radioimmunotherapy.

PURPOSE: Many cancer treatments suffer from dose-limiting toxicities to vital organs due to poor therapeutic indices. To overcome these challenges we developed a novel multimerization platform that rapidly removes tumor-targeting proteins from the blood to substantially improve therapeutic index. EXPERIMENTAL DESIGN: The platform was designed as a fusion of a self-assembling and disassembling (SADA) domain to a tandem single-chain bispecific antibody (BsAb, anti-ganglioside GD2 × anti-DOTA). SADA-BsAbs were assessed with multiple in vivo tumor models using two-step pretargeted radioimmunotherapy (PRIT) to evaluate tumor uptake, dosimetry, and antitumor responses. RESULTS: SADA-BsAbs self-assembled into stable tetramers (220 kDa), but could also disassemble into dimers or monomers (55 kDa) that rapidly cleared via renal filtration and substantially reduced immunogenicity in mice. When used with rapidly clearing DOTA-caged PET isotopes, SADA-BsAbs demonstrated accurate tumor localization, dosimetry, and improved imaging contrast by PET/CT. When combined with therapeutic isotopes, two-step SADA-PRIT safely delivered massive doses of alpha-emitting (225Ac, 1.48 MBq/kg) or beta-emitting (177Lu, 6,660 MBq/kg) S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (DOTA) payloads to tumors, ablating them without any short-term or long-term toxicities to the bone marrow, kidneys, or liver. CONCLUSIONS: The SADA-BsAb platform safely delivered large doses of radioisotopes to tumors and demonstrated no toxicities to the bone marrow, kidneys, or liver. Because of its modularity, SADA-BsAbs can be easily adapted to most tumor antigens, tumor types, or drug delivery approaches to improve therapeutic index and maximize the delivered dose.See related commentary by Capala and Kunos, p. 377.

Targeting Germline- and Tumor-Associated Nucleotide Excision Repair Defects in Cancer.

PURPOSE: Nucleotide excision repair (NER) gene alterations constitute potential cancer therapeutic targets. We explored the prevalence of NER gene alterations across cancers and putative therapeutic strategies targeting these vulnerabilities. EXPERIMENTAL DESIGN: We interrogated our institutional dataset with mutational data from more than 40,000 patients with cancer to assess the frequency of putative deleterious alterations in four key NER genes. Gene-edited isogenic pairs of wild-type and mutant ERCC2 or ERCC3 cell lines were created and used to assess response to several candidate drugs. RESULTS: We found that putative damaging germline and somatic alterations in NER genes were present with frequencies up to 10% across multiple cancer types. Both in vitro and in vivo studies showed significantly enhanced sensitivity to the sesquiterpene irofulven in cells harboring specific clinically observed heterozygous mutations in ERCC2 or ERCC3. Sensitivity of NER mutants to irofulven was greater than to a current standard-of-care agent, cisplatin. Hypomorphic ERCC2/3-mutant cells had impaired ability to repair irofulven-induced DNA damage. Transcriptomic profiling of tumor tissues suggested codependencies between DNA repair pathways, indicating a potential benefit of combination therapies, which were confirmed by in vitro studies. CONCLUSIONS: These findings provide novel insights into a synthetic lethal relationship between clinically observed NER gene deficiencies and sensitivity to irofulven and its potential synergistic combination with other drugs.See related commentary by Jiang and Greenberg, p. 1833.

Alpha radioimmunotherapy using 225Ac-proteus-DOTA for solid tumors - safety at curative doses.

This is the initial report of an α-based pre-targeted radioimmunotherapy (PRIT) using 225Ac and its theranostic pair, 111In. We call our novel tumor-targeting DOTA-hapten PRIT system "proteus-DOTA" or "Pr." Herein we report the first results of radiochemistry development, radiopharmacology, and stoichiometry of tumor antigen binding, including the role of specific activity, anti-tumor efficacy, and normal tissue toxicity with the Pr-PRIT approach (as α-DOTA-PRIT). A series of α-DOTA-PRIT therapy studies were performed in three solid human cancer xenograft models of colorectal cancer (GPA33), breast cancer (HER2), and neuroblastoma (GD2), including evaluation of chronic toxicity at ~20 weeks of select survivors. Methods: Preliminary biodistribution experiments in SW1222 tumor-bearing mice revealed that 225Ac could not be efficiently pretargeted with current DOTA-Bn hapten utilized for 177Lu or 90Y, leading to poor tumor uptake in vivo. Therefore, we synthesized Pr consisting of an empty DOTA-chelate for 225Ac, tethered via a short polyethylene glycol linker to a lutetium-complexed DOTA for picomolar anti-DOTA chelate single-chain variable fragment (scFv) binding. Pr was radiolabeled with 225Ac and its imaging surrogate, 111In. In vitro studies verified anti-DOTA scFv recognition of [225Ac]Pr, and in vivo biodistribution and clearance studies were performed to evaluate hapten suitability and in vivo targeting efficiency. Results: Intravenously (i.v.) administered 225Ac- or 111In-radiolabeled Pr in mice showed rapid renal clearance and minimal normal tissue retention. In vivo pretargeting studies show high tumor accumulation of Pr (16.71 ± 5.11 %IA/g or 13.19 ± 3.88 %IA/g at 24 h p.i. for [225Ac]Pr and [111In]Pr, respectively) and relatively low uptake in normal tissues (all average ≤ 1.4 %IA/g at 24 h p.i.). Maximum tolerated dose (MTD) was not reached for either [225Ac]Pr alone or pretargeted [225Ac]Pr at administered activities up to 296 kBq/mouse. Single-cycle treatment consisting of α-DOTA-PRIT with either huA33-C825 bispecific anti-tumor/anti-DOTA-hapten antibody (BsAb), anti-HER2-C825 BsAb, or hu3F8-C825 BsAb for targeting GPA33, HER2, or GD2, respectively, was highly effective. In the GPA33 model, no complete responses (CRs) were observed but prolonged overall survival of treated animals was 42 d for α-DOTA-PRIT vs. 25 d for [225Ac]Pr only (P < 0.0001); for GD2, CRs (7/7, 100%) and histologic cures (4/7, 57%); and for HER2, CRs (7/19, 37%) and histologic cures (10/19, 56%) with no acute or chronic toxicity. Conclusions: [225Ac]Pr and its imaging biomarker [111In]Pr demonstrate optimal radiopharmacologic behavior for theranostic applications of α-DOTA-PRIT. For this initial evaluation of efficacy and toxicity, single-cycle treatment regimens were performed in all three systems. Histologic toxicity was not observed, so MTD was not observed. Prolonged overall survival, CRs, and histologic cures were observed in treated animals. In comparison to RIT with anti-tumor IgG antibodies, [225Ac]Pr has a much improved safety profile. Ultimately, these data will be used to guide clinical development of toxicity and efficacy studies of [225Ac]Pr, with the goal of delivering massive lethal doses of radiation to achieve a high probability of cure without toxicity.

Synthesis of the PET Tracer 124I-Trametinib for MAPK/ERK Kinase Distribution and Resistance Monitoring.

Trametinib is an extremely potent allosteric inhibitor of mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) (MEK) 1/2, which has been approved for treatment of metastatic melanoma and anaplastic thyroid cancer in patients with confirmed BRAFV600E/K mutations. Though trametinib is highly efficacious, adverse side effects, including skin, gastrointestinal, and hepatic toxicity, are dose-limiting and can lead to treatment termination. Development of a noninvasive tool to visualize and quantify the delivery and distribution of trametinib (either as a single agent or in combination with other therapeutics) to tumors and organs would be helpful in assessing therapeutic index, personalizing individual dose, and potentially predicting resistance to therapy. Methods: To address these issues, we have developed a radiolabeled trametinib and evaluated the in vitro and in vivo properties. 123I-, 124I-, and 131I-trametinib, pure tracer analogs to trametinib, were synthesized in more than 95% purity, with an average yield of 69.7% and more than 100 GBq/µmol specific activity. Results: Overall, 124I-trametinib uptake in a panel of cancer cell lines can be blocked with cold trametinib, confirming specificity of the radiotracer in vitro and in vivo. 124I-trametinib was taken up at higher rates in KRAS and BRAF mutant cell lines than in wild-type KRAS cancer cell lines. In vivo, biodistribution revealed high uptake in the liver 2 h after injection, followed by clearance through the gastrointestinal tract over 4 d. Importantly, uptake higher than expected was observed in the lung and heart for up to 24 h. Peak uptake in the skin and gastrointestinal tract was observed between 6 and 24 h, whereas in B16F10 melanoma-bearing mice peak tumor concentrations were achieved between 24 and 48 h. Tumor uptake relative to muscle and skin was relatively low, peaking at 3.4- to 8.1-fold by 72 h, respectively. The biodistribution of 124I-trametinib was significantly reduced in mice on trametinib therapy, providing a quantitative method to observe MEK inhibition in vivo. Conclusion:124I-trametinib serves as an in vivo tool to personalize the dose instead of using the current single-fixed-dose scheme and, when combined with radiomic data, to monitor the emergence of therapy resistance. In addition, the production of iodinated trametinib affords researchers the ability to measure drug distribution for improved drug delivery studies.

An N-Acetylgalactosamino Dendron-Clearing Agent for High-Therapeutic-Index DOTA-Hapten Pretargeted Radioimmunotherapy.

Clearing agents (CAs) can rapidly remove nonlocalized targeting biomolecules from circulation for hepatic catabolism, thereby enhancing the therapeutic index (TI), especially for blood (marrow), of the subsequently administered radioisotope in any multistep pretargeting strategy. Herein we describe the synthesis and in vivo evaluation of a fully synthetic glycodendrimer-based CA for DOTA-based pretargeted radioimmunotherapy (DOTA-PRIT). The novel dendron-CA consists of a nonradioactive yttrium-DOTA-Bn molecule attached via a linker to a glycodendron displaying 16 terminal α-thio-N-acetylgalactosamine (α-SGalNAc) units (CCA α-16-DOTA-Y3+; molecular weight: 9059 Da). Pretargeting [177Lu]LuDOTA-Bn with CCA α-16-DOTA-Y3+ to GPA33-expressing SW1222 human colorectal xenografts was highly effective, leading to absorbed doses of [177Lu]LuDOTA-Bn for blood, tumor, liver, spleen, and kidneys of 11.7, 468, 9.97, 5.49, and 13.3 cGy/MBq, respectively. Tumor-to-normal tissues absorbed-dose ratios (i.e., TIs) ranged from 40 (e.g., for blood and kidney) to about 550 for stomach.

A Small-Molecule Pan-Id Antagonist Inhibits Pathologic Ocular Neovascularization.

Id helix-loop-helix (HLH) proteins (Id1-4) bind E protein bHLH transcription factors, preventing them from forming active transcription complexes that drive changes in cell states. Id proteins are primarily expressed during development to inhibit differentiation, but they become re-expressed in adult tissues in diseases of the vasculature and cancer. We show that the genetic loss of Id1/Id3 reduces ocular neovascularization in mouse models of wet age-related macular degeneration (AMD) and retinopathy of prematurity (ROP). An in silico screen identifies AGX51, a small-molecule Id antagonist. AGX51 inhibits the Id1-E47 interaction, leading to ubiquitin-mediated degradation of Ids, cell growth arrest, and reduced viability. AGX51 is well-tolerated in mice and phenocopies the genetic loss of Id expression in AMD and ROP models by inhibiting retinal neovascularization. Thus, AGX51 is a first-in-class compound that antagonizes an interaction formerly considered undruggable and that may have utility in the management of multiple diseases.

The Polycomb Repressor Complex 1 Drives Double-Negative Prostate Cancer Metastasis by Coordinating Stemness and Immune Suppression.

The mechanisms that enable immune evasion at metastatic sites are poorly understood. We show that the Polycomb Repressor Complex 1 (PRC1) drives colonization of the bones and visceral organs in double-negative prostate cancer (DNPC). In vivo genetic screening identifies CCL2 as the top prometastatic gene induced by PRC1. CCL2 governs self-renewal and induces the recruitment of M2-like tumor-associated macrophages and regulatory T cells, thus coordinating metastasis initiation with immune suppression and neoangiogenesis. A catalytic inhibitor of PRC1 cooperates with immune checkpoint therapy to reverse these processes and suppress metastasis in genetically engineered mouse transplantation models of DNPC. These results reveal that PRC1 coordinates stemness with immune evasion and neoangiogenesis and point to the potential clinical utility of targeting PRC1 in DNPC.

CRISPR-Cas III-A Csm6 CARF Domain Is a Ring Nuclease Triggering Stepwise cA4 Cleavage with ApA>p Formation Terminating RNase Activity.

Type III-A CRISPR-Cas surveillance complexes containing multi-subunit Csm effector, guide, and target RNAs exhibit multiple activities, including formation of cyclic-oligoadenylates (cAn) from ATP and subsequent cAn-mediated cleavage of single-strand RNA (ssRNA) by the trans-acting Csm6 RNase. Our structure-function studies have focused on Thermococcus onnurineus Csm6 to deduce mechanistic insights into how cA4 binding to the Csm6 CARF domain triggers the RNase activity of the Csm6 HEPN domain and what factors contribute to regulation of RNA cleavage activity. We demonstrate that the Csm6 CARF domain is a ring nuclease, whereby bound cA4 is stepwise cleaved initially to ApApApA>p and subsequently to ApA>p in its CARF domain-binding pocket, with such cleavage bursts using a timer mechanism to regulate the RNase activity of the Csm6 HEPN domain. In addition, we establish T. onnurineus Csm6 as an adenosine-specific RNase and identify a histidine in the cA4 CARF-binding pocket involved in autoinhibitory regulation of RNase activity.